In a manufacturing process of a semiconductor device, various films having different physical properties are formed on a silicon substrate and these films are subjected to various processes, thus forming fine metal interconnects. For example, in a damascene interconnect forming process, interconnect trenches are formed in a film, and the interconnect trenches are then filled with metal. Thereafter, an unnecessary metal is removed by chemical mechanical polishing (CMP), so that metal interconnects are formed. A variety of films including a metal film, a barrier film, and a dielectric film exist on a surface of the substrate that has been manufactured through such a damascene interconnect forming process.
A CMP apparatus (polishing apparatus) for polishing a substrate is typically configured to not only polish a substrate, but also clean and dry the polished substrate. Cleaning of the substrate is performed by bringing a cleaning tool, such as a roll sponge, into sliding contact with the substrate while rotating the substrate. After cleaning of the substrate, ultrapure water (DIW) is supplied onto the rotating substrate, thereby rinsing the substrate. Before the substrate is dried, the ultrapure water is further supplied onto the rotating substrate to rinse the substrate.
It is commonly known that the ultrapure water, to be supplied onto the rotating substrate, has a high specific resistance value (≧15M Ω·cm) and that the surface of the substrate is electrostatically charged by the contact with the ultrapure water. Practically, experiments have confirmed that the surface of the substrate, on which metal interconnects and dielectric films are formed, is electrostatically charged as a result of the contact with the ultrapure water. Possible causes of such a phenomenon of the electrostatic charge may include the fact that the ultrapure water has a high specific resistance value and that the ultrapure water forms a flow on the rotating substrate, although the causes are uncertain. The electrostatic charge of the substrate surface may cause reattachment of particles that have been once removed by the cleaning process of the substrate surface, and may cause destruction of devices due to electrostatic discharge. Further, in devices having copper interconnects, copper (Cu) itself is liable to migrate under the influence of the surface charge, and may be attached to a dielectric film. Consequently, shortcut between the interconnects or leakage of current may occur, and/or poor adhesion between the copper interconnects and the dielectric film may occur.
Since the electrostatic charge of the substrate surface can lower a reliability of the devices, it is necessary to measure an amount of static electricity, i.e., a surface potential, and monitor it. However, a conventional device for measuring the surface potential of the substrate is very expensive. As a result, device fabrication costs will increase. Moreover, the surface potential of the substrate is likely to change due to various external factors. For example, separation charge, induction charge, and atmospheric charge may affect measurement of the surface potential of the substrate. Consequently, it has been difficult to precisely measure an accurate surface potential so far.